Development of angle-resolved spectroscopy system of electrons emitted from a surface with negative electron affinity state

Abstract

We developed an angle-resolved photoemission spectroscopy system for the analysis of conduction-band electrons. By forming a negative electron affinity surface on a semiconductor surface, electrons in conduction bands are emitted into a vacuum and measured by using an analyzer. This method enables us to determine the energy and momentum of the conduction electrons. Furthermore, it can be used to determine unoccupied conduction band structures. The main challenges of this method are that the energies of the emitted electrons are extremely low and the trajectories of the electrons change due to various influences. We overcame these problems by placing the shielding mesh close to the sample and parallel to the sample surface. The entire chambers, including the shielding mesh, were grounded, and a negative bias voltage was applied only to the sample. This configuration realizes the acceleration of electrons while preserving the momentum component parallel to the sample surface. Another problem is the establishment of a method for converting a detected angle into the corresponding wavevector. We focused on the emission angle of electrons emitted from a sample and their minimum energy and then established an analytical method for converting detected angles into corresponding wavevectors on the basis of the minimum energy.

Expanding the momentum field of view in angle-resolved photoemission systems with hemispherical analyzers

“…As we demonstrate, a symmetric bias field between the sample, its holder and the analyzer can be obtained by careful engineering of the experimental design. Other objects near the photoelectron trajectory, such as the capillary of a Helium lamp can cause significant field distortions 19 and a different design with its own angle-to-momentum conversion formalism might be necessary. 19,20 We also note that samples with large flat surfaces are preferred to obtain a uniform electric field.…”

“…Other objects near the photoelectron trajectory, such as the capillary of a Helium lamp can cause significant field distortions 19 and a different design with its own angle-to-momentum conversion formalism might be necessary. 19,20 We also note that samples with large flat surfaces are preferred to obtain a uniform electric field. The investigation of samples with rough surfaces is more challenging due to irregular fields near the surface.…”

“…Accordingly, recent implementations feature an electrically grounded mesh near the sample to minimize distortions of the electric field, however putting constraints on the incidence of the light source. 19,20 In this work, we describe an implementation of sample bias for a setup with a conventional hemispherical analyzer as widely used in the photoemission community. We demonstrate access to the largest emitted momenta in a single experimental geometry using a 6 eV laser light source.…”